1. Field of the Invention
The invention relates to an electromagnetic rotary drive including a driven rotor and an electric motor that includes a stator and driving rotor. The invention further relates to pumps and stirring machines driven by rotary drives of this kind.
2. Description of the Prior Art
Rotary pumps with hermetically closed pump housings are used when a complete separation of the fluid to be conveyed from the surroundings is required. Although this requirement would be more easily fulfilled by hose squeezing pumps than by rotary pumps, hose squeezing pumps, so-called peristaltic pumps can frequently not be used because shear forces act on the fluid during their operation by virtue of their specific construction through which the structure of the fluid is impaired. In pharmaceutical and medical fields of application in particular, where mechanically sensitive fluids with long molecular chains or with cells having sensitive cell membranes are to be forwarded, it is necessary to use rotary pumps. In pumping blood, for example, there is the danger that a hemolysis arises as a result of such shear forces, which renders the blood unusable. In contrast to the situation with piston pumps, the fluids are exposed to practically no shear forces in centrifugal pumps so that long molecules with sensitive cells are protected when being conveyed.
A strict material isolation of the fluid to be forwarded can be necessary for two different reasons: on the one hand, an outflow of even the smallest amounts of fluid to the surroundings is to be rendered impossible thereby when contaminating substances are forwarded; on the other hand, an intrusion of foreign substances of any kind into the fluid is to be prevented when the latter must satisfy the highest requirements with respect to purity, which is above all the case when using the pump in the chemical, pharmaceutical or medical fields. Especially for these fields of application, the material isolation of the fluid to be forwarded consists not only in making the intrusion of the surrounding air impossible, but rather particles abraded from relatively moving components of the drive device, of the bearing arrangement or of a sealing arrangement, and lubricants should also be prevented from entering into the fluid.
Pumps of the initially named kind are used during open heart surgery for maintaining the blood circulation, with the fluid to be forwarded being the blood of the patient. It is self evident that in such cases the highest demands are made with respect to maintaining the purity of the fluid to be pumped.
When using conventional drive devices, bearing devices and sliding ring seals, it proved impossible to seal off the pump housing completely relative to the surroundings and at the same time to prevent the production of abraded particles from relatively moved components and the intrusion of such abrasion particles and of lubricants into the fluid.
By means of the magnetic bearings known for a longer period of time, it was possible to replace conventional roller or sliding bearings by a bearing apparatus which enables not only contact-free journalling, for example in the form of a buoyant sliding bearing, but also enables lubricant-free journalling.
A further advance in the same direction is the development of three phase current motors with a separation of the stator from the rotor, so-called split tube motors.
For example, EP-0 551 435 describes an electromagnetic rotary drive for a rotary pump with a hermetically sealed pump housing and a pump rotor which is journalled by means of a contact-free bearing device and is driven by a split tube motor.
This electromagnetic rotary drive for the pump is constructed in a complicated and expensive manner and is relatively voluminous, with its axial dimension in particular being large. The magnetic bearings require a large amount of space.